Crack Paths 2009

Direct incorporation of homogenized MD-models:

• Modeling and simulation of the molecular structure,

• Homogenization in a unit cell,

• Use it inside a macro-model.

• Such approaches could also base on FEM-or semi-analytical representations of

the micro-structure – the field of meso-mechanics.

Extraction of mechanical properties for use in F E M :

• Modeling of the molecular structure,

• Simulations towards extraction of key-properties, (Young’s modulus, CTE,

diffusion coefficients – see Figure 5)

• Use these properties in a macro-model, a FE-model for instance – see [12].

Figure 5. MD-simulation to extract moisture diffusion coefficients [12]

Because of the wide gap between M Dand F E Mand also because of the huge amount

of computational resources necessary for appropriate M Dsimulations, the second way

is preferred at the moment.

M U L T I P LFEA I L U R EV A L U A T I O N

Miniaturization, new materials and harsh environmental conditions cause new chal

lenges for reliability analysis and prediction, i.e. the development of multiple failure

criteria for combined loadings like residual stresses generated by several steps of the

manufacturing process, various kinds of inhomogeneity, moisture diffusion and the well

known thermal expansion mismatch problem. These circumstances, which can cause

different failure modes like interface delamination, chip or encapsulation cracking, pop

corning and/or fatigue of interconnects, have to be treated on a new qualitative level.

Traditionally applied methodologies base on classical strength evaluations or/and life

time estimations of solder interconnects by means of modified Coffin-Manson ap

proaches, which rarely address multiple failure modes. Second, especially under cyclic

loading conditions, fatigue of solder materials, fatigue crack propagation in polymers or

at bimaterial interfaces and ratcheting of kinematic hardening metals take effect simul

taneously. Therefore, approaches to evaluate such risks and damage propagation rates

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